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High Negative Long Term Fuel Trims - 00 Ranger 3.0L


fast240z

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If all the sensors are reading correctly and the fuel pressure/injectors are within computers parameters then only conclusion for a fuel trim error will be computer internal error

If you fix a fuel trim error it can take a week or two for LTFT to come back to +/- 5%
Would resetting KAM allow LTFT to show correct values faster?
 


bills4065

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Here is what Mitchell says for the trims on a 3.0 Litre Ranger. LTFT -20 to + 20. STFT -10 to +10. Those same numbers apply to both banks. Just sharing what my Mitchell subscription says for the fuel trims.
 

RonD

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Yes, if those trims are not exceeded then no Trouble codes as those are "acceptable" as an engine/system ages gracefully

You can try clearing keep alive memory(KAM) but not sure you can with a regular scanner, I know Ford scanners could reset LTFT
The whole point of LTFT is so engine/system can age gracefully and computer doesn't have to 're-learn" fuel trims at each start up, so for DIY its not a good thing to do if you don't know what will happen after its reset to 0

LTFT is so engine can run OK at cold start before O2s are on-line, computer has no feedback from O2s on cold start, so engine "may" run poorly after clearing LTFT and cold start, so just a heads up, once O2s get hot enough to work, 3-5min, then computer can adjust fuel trims and start re-learning the system and rebuild LTFT
 

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You can have a baro PID and not have a sensor.

Is it possible your new injectors are wrong?
 

fast240z

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Yes, if those trims are not exceeded then no Trouble codes as those are "acceptable" as an engine/system ages gracefully

You can try clearing keep alive memory(KAM) but not sure you can with a regular scanner, I know Ford scanners could reset LTFT
The whole point of LTFT is so engine/system can age gracefully and computer doesn't have to 're-learn" fuel trims at each start up, so for DIY its not a good thing to do if you don't know what will happen after its reset to 0

LTFT is so engine can run OK at cold start before O2s are on-line, computer has no feedback from O2s on cold start, so engine "may" run poorly after clearing LTFT and cold start, so just a heads up, once O2s get hot enough to work, 3-5min, then computer can adjust fuel trims and start re-learning the system and rebuild LTFT
OK perfect, I reset KAM using IDS yesterday so LTFT should be accurate.

I pulled the exhaust today and the cats are fine. You can see light through the honeycomb so they're not plugged.
 

fast240z

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You can have a baro PID and not have a sensor.

Is it possible your new injectors are wrong?
Possibly, but I don't think so. The issue with the high LTFT and crazy STFT existed before the injectors were swapped. The main reason I changed injectors is because they were leaking when testing fuel pressure KOEO.
 

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What's the engine vacuum at idle?
 

bills4065

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Hey all just want to throw this in here. here is a great article on MAF sensor diagnosis . Try this on a google search: Successful MAF sensor Diagnosis Motor. It was a July 2006 article . They do talk a fair bit about ford vehicles.
 

ggf

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I have a 2000 3.0L FFV that is having high negative long term fuel trims at idle, and I'm not sure what to troubleshoot next. The trims stabilize around -8 LTFT/+2 STFT when driving, but will spike to -15 after pulling off the freeway and idling.

I bought the truck 5 years ago and discovered it was misfiring badly due to low compression from bad valve seats (common 3.0 issue). A rebuilt set of heads fixed the issue and the truck ran fine. Last year, the heater hose coupling failed and I lost all coolant and warped the heads. I resurfaced the heads and truck has been running fine once again. Recently it started running a little rough at idle and I'm trying to track down the root cause.

I've performed the following troubleshooting items:
  1. New O2 sensors - both upstream and downstream. Originals were very slow to update and were biased rich.
  2. New idle air control valve
  3. Fuel pressure test from fuel rail - 59 psi KOER, 50 psi KOEO. Pressure would hold with key on but would immediately leak down after turning key off. Fuel trims/O2 showed very rich on both banks, and replacement injectors fixed leakdown.
  4. New injectors - old ones failed leakdown, cleaning didn't fix issue.
  5. Smoke test on intake - smoke leaked from EGR valve, replaced EGR. No other leaks found.
  6. New Intake air temp sensor - original was stuck hot
  7. New coil pack, plugs, and motorcraft wires - original plugs were toast and old coil pack had cracks in it
  8. Replacement MAF from Autozone - original looked slightly burnt and BARO value was slow to update
The only other issue I can think of is maybe plugged exhaust. The misfire and leaking injectors make me suspect the catalytic converters are plugged, but the truck accelerates to redline fine.


Driving at cruising speed -
View attachment 58496


After exiting freeway and sitting at idle:

View attachment 58497



WOT in 4th gear-
View attachment 58498
So right now 95 3.0 is running a little lean and im trying to figure out the proper fuel trim percentages before I go and start replacing the O2 sensors my long term stays at 25% for both banks and my short for bank bounces between 4 and 12 and bank 2 bounces between 4 and 13, do I have proper fuel trim?
 

bills4065

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Long term 25% on both banks. Is this while truck is at idle?
 

RonD

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So right now 95 3.0 is running a little lean and im trying to figure out the proper fuel trim percentages before I go and start replacing the O2 sensors my long term stays at 25% for both banks and my short for bank bounces between 4 and 12 and bank 2 bounces between 4 and 13, do I have proper fuel trim?
You should start your own thread

There are no valid fuel trims at idle, as said, only while cruising at a steady speed
-5% to +5% is expected for STFT

Long term +25% LTFT, means your STFT has been high for awhile
And the +25% should set a Lean code

But STFT and LTFT are only valid if O2 sensors are all under 100k miles or under 12 years old, 1995 3.0l should have 3 O2 sensors
Otherwise looking at fuel trims are a waste of time
O2s are the only thing the computer has to get/set fuel trims
 
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